Chemically Induced Dynamic Nuclear Polarization (CIDNP) is a nuclear magnetic resonance (nmr) phenomenon which produces very large changes in the intensities of nmr signals from samples undergoing radical pair reactions. This method can be used to probe protein structure and dynamics by using photo-induced hydrogen abstraction or electron transfer reactions involving histidine, tyrosine and tryptophan residues. The amino acid selectivity of the photochemical reaction greatly enhances the information content of high resolution nmr spectra of macromolecules. A 360 MHz 1H nmr spectrometer has been modified to permit laser irradiation of the sample under computer control. Water and lipid soluble dyes will be developed which extend the method to non-polar regions of biological membranes. This method will be used to determine the positions of tryptophan residues in the small peptide ion-channel gramicidin in vesicles and conformational changes which accompany ion transport. Radical pair dynamics can be used to study the effect of a reduction of dimensionality on chemical reactions in anisotropic bilayers. The photolability of tryptophan in proteins will be exploited by CIDNP to probe the surface accessibility of the residue and the structural requirements for efficient electron transfer. The photo-CIDNP method can be used to measure selective spin-lattice relaxation rates (I/T1) in proteins using the hv-t-90 pulse sequence. This technique will be applied to measure internal motion of diamagnetic porphyrins and chlorophylls in apo-myoglobin (the chloroglobins).